UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Reply
 
Thread Tools
Old 28th Sep 2020, 5:10 pm   #1
jmcilkley
Triode
 
Join Date: Jan 2020
Location: Ilkley, West Yorkshire, UK.
Posts: 23
Default Sony ST242L tuner works on only half the frequency range

I'm trying to resurrect a Sony ST242L. When I started it didn't tune to anything at all but liberal use of de-ox on the band selector brought it back to life. It now works perfectly but only on half the range. 98MHz up is fine but below 98 it stays on the same channel.
This is an ususual design in that the tuning is done inside a program sensor unit so no visible tuning condenser. I have the service manual (attached) but it gives no clue as to what goes on inside this module so i don't know where to start looking. I wonder if anyone has experience with this unusual method and can give any pointers?
Sorry, can't upload the manual as it is too big but it's available on that wonderful site :
https://elektrotanya.com/sony_st-242l.pdf/download.html
jmcilkley is offline   Reply With Quote
Old 28th Sep 2020, 7:50 pm   #2
Herald1360
Dekatron
 
Herald1360's Avatar
 
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 14,761
Default Re: Sony ST242L tuner works on only half the frequency range

The program sensor doesn't do the actual tuning, that's done by the varicap diodes in the FM front end. However, they get their variable tuning voltage via that mysterious block.

Is it a sealed unit or are its components accessible?

Have you checked that the high and low limit tuning voltages fed to the program sensor are correct?
__________________
....__________
....|____||__|__\_____
.=.| _---\__|__|_---_|.
.........O..Chris....O
Herald1360 is offline   Reply With Quote
Old 28th Sep 2020, 10:56 pm   #3
jmcilkley
Triode
 
Join Date: Jan 2020
Location: Ilkley, West Yorkshire, UK.
Posts: 23
Default Re: Sony ST242L tuner works on only half the frequency range

No - that was going to be my first check unless someone had a better idea. The sensor can be removed quite easily but needs to be disconnected from the tuning dial string. I can't tell if it's accessible until I take it out.
jmcilkley is offline   Reply With Quote
Old 29th Sep 2020, 10:18 am   #4
jmcilkley
Triode
 
Join Date: Jan 2020
Location: Ilkley, West Yorkshire, UK.
Posts: 23
Default Re: Sony ST242L tuner works on only half the frequency range

OK, checked the voltages and the low end is way too high and the variable resistor that is supposed to adjust it has no effect (but the vr checks out ok for resistance). The top end and middle show the correct voltages. I guess that means that something is wrong in the program sensor unit so that will be the next step to remove that and see what's inside.
jmcilkley is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 3:26 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.